In the drilling and completion industry, fiber optic cables and sensors have become very important in maximizing efficiency in all phases of well construction and development. Real time information provided by the fibers allows operators to make prescient decisions that reduce errors and delays. Fiber has been growing in use for at least a decade and now can be found in many downhole tools and systems.
While the industry is generally enamored of pursuing the use of fiber, there are still issues surrounding its use that are detractors. For example, hydrogen darkening is an issue that has plagued the industry for years, particularly with respect to Distributed Temperature Sensor (DTS) arrangements operated in a single end mode. This is because Raman scattered light has a very wavelength dependent absorption spectrum. Since different components of the Raman signals get attenuated at different rates, the temperature traces computed from the Raman scatter data contain artifacts due to the hydrogen absorption features. Efforts have been made to render the fiber resistant to hydrogen infiltration to alleviate these effects but the previously tried measures have only been partially effective. When darkening occurs, stokes wavelengths are unaffected while antistokes wavelengths are inconsistently affected. This results in readings that are unreliable. Despite the efforts noted above, the problem persists. The art would welcome alternative approaches that render use of fiber more reliable in such circumstances.